src/exif.c

// Copyright 2022 Google LLC. All rights reserved.
// SPDX-License-Identifier: BSD-2-Clause

#include "avif/internal.h"

#include <stdint.h>
#include <string.h>

avifResult avifGetExifTiffHeaderOffset(const avifRWData * exif, uint32_t * offset)
{
    const uint8_t tiffHeaderBE[4] = { 'M', 'M', 0, 42 };
    const uint8_t tiffHeaderLE[4] = { 'I', 'I', 42, 0 };
    for (*offset = 0; *offset + 4 < exif->size; ++*offset) {
        if (!memcmp(&exif->data[*offset], tiffHeaderBE, 4) || !memcmp(&exif->data[*offset], tiffHeaderLE, 4)) {
            return AVIF_RESULT_OK;
        }
    }
    // Couldn't find the TIFF header
    return AVIF_RESULT_INVALID_EXIF_PAYLOAD;
}

avifResult avifImageExtractExifOrientationToIrotImir(avifImage * image)
{
    const avifTransformFlags otherFlags = image->transformFlags & ~(AVIF_TRANSFORM_IROT | AVIF_TRANSFORM_IMIR);
    uint32_t offset;
    const avifResult result = avifGetExifTiffHeaderOffset(&image->exif, &offset);
    if (result != AVIF_RESULT_OK) {
        // Couldn't find the TIFF header
        return result;
    }

    avifROData raw = { image->exif.data + offset, image->exif.size - offset };
    const avifBool littleEndian = (raw.data[0] == 'I');
    avifROStream stream;
    avifROStreamStart(&stream, &raw, NULL, NULL);

    // TIFF Header
    uint32_t offsetTo0thIfd;
    if (!avifROStreamSkip(&stream, 4) || // Skip tiffHeaderBE or tiffHeaderLE.
        !avifROStreamReadU32Endianness(&stream, &offsetTo0thIfd, littleEndian)) {
        return AVIF_RESULT_INVALID_EXIF_PAYLOAD;
    }

    avifROStreamSetOffset(&stream, offsetTo0thIfd);
    uint16_t fieldCount;
    if (!avifROStreamReadU16Endianness(&stream, &fieldCount, littleEndian)) {
        return AVIF_RESULT_INVALID_EXIF_PAYLOAD;
    }
    for (uint16_t field = 0; field < fieldCount; ++field) { // for each field interoperability array
        uint16_t tag;
        uint16_t type;
        uint32_t count;
        uint16_t firstHalfOfValueOffset;
        if (!avifROStreamReadU16Endianness(&stream, &tag, littleEndian) || !avifROStreamReadU16Endianness(&stream, &type, littleEndian) ||
            !avifROStreamReadU32Endianness(&stream, &count, littleEndian) ||
            !avifROStreamReadU16Endianness(&stream, &firstHalfOfValueOffset, littleEndian) || !avifROStreamSkip(&stream, 2)) {
            return AVIF_RESULT_INVALID_EXIF_PAYLOAD;
        }
        // Orientation attribute according to JEITA CP-3451C section 4.6.4 (TIFF Rev. 6.0 Attribute Information):
        const uint16_t shortType = 0x03;
        if (tag == 0x0112 && type == shortType && count == 0x01) {
            // Mapping from Exif orientation as defined in JEITA CP-3451C section 4.6.4.A Orientation
            // to irot and imir boxes as defined in HEIF ISO/IEC 28002-12:2021 sections 6.5.10 and 6.5.12.
            switch (firstHalfOfValueOffset) {
                case 1: // The 0th row is at the visual top of the image, and the 0th column is the visual left-hand side.
                    image->transformFlags = otherFlags;
                    image->irot.angle = 0; // ignored
                    image->imir.mode = 0;  // ignored
                    return AVIF_RESULT_OK;
                case 2: // The 0th row is at the visual top of the image, and the 0th column is the visual right-hand side.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IMIR;
                    image->irot.angle = 0; // ignored
                    image->imir.mode = 1;
                    return AVIF_RESULT_OK;
                case 3: // The 0th row is at the visual bottom of the image, and the 0th column is the visual right-hand side.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IROT;
                    image->irot.angle = 2;
                    image->imir.mode = 0; // ignored
                    return AVIF_RESULT_OK;
                case 4: // The 0th row is at the visual bottom of the image, and the 0th column is the visual left-hand side.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IMIR;
                    image->irot.angle = 0; // ignored
                    image->imir.mode = 0;
                    return AVIF_RESULT_OK;
                case 5: // The 0th row is the visual left-hand side of the image, and the 0th column is the visual top.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IROT | AVIF_TRANSFORM_IMIR;
                    image->irot.angle = 1; // applied before imir according to MIAF spec ISO/IEC 28002-12:2021 - section 7.3.6.7
                    image->imir.mode = 0;
                    return AVIF_RESULT_OK;
                case 6: // The 0th row is the visual right-hand side of the image, and the 0th column is the visual top.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IROT;
                    image->irot.angle = 3;
                    image->imir.mode = 0; // ignored
                    return AVIF_RESULT_OK;
                case 7: // The 0th row is the visual right-hand side of the image, and the 0th column is the visual bottom.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IROT | AVIF_TRANSFORM_IMIR;
                    image->irot.angle = 3; // applied before imir according to MIAF spec ISO/IEC 28002-12:2021 - section 7.3.6.7
                    image->imir.mode = 0;
                    return AVIF_RESULT_OK;
                case 8: // The 0th row is the visual left-hand side of the image, and the 0th column is the visual bottom.
                    image->transformFlags = otherFlags | AVIF_TRANSFORM_IROT;
                    image->irot.angle = 1;
                    image->imir.mode = 0; // ignored
                    return AVIF_RESULT_OK;
                default: // reserved
                    break;
            }
        }
    }
    // Orientation is in the 0th IFD, so no need to parse the following ones.

    // The orientation tag is not mandatory (only recommended) according to JEITA CP-3451C section 4.6.8.A.
    // The default value is 1 if the orientation tag is missing, meaning:
    //   The 0th row is at the visual top of the image, and the 0th column is the visual left-hand side.
    image->transformFlags = otherFlags;
    image->irot.angle = 0; // ignored
    image->imir.mode = 0;  // ignored
    return AVIF_RESULT_OK;
}

void avifImageSetMetadataExif(avifImage * image, const uint8_t * exif, size_t exifSize)
{
    avifRWDataSet(&image->exif, exif, exifSize);
    // Ignore any Exif parsing failure.
    (void)avifImageExtractExifOrientationToIrotImir(image);
}